There exist at the present a number of devices for measuring the running of watches. The best known is the chronograph comparator which allows printing, on a band of paper, the phase difference between an internal reference frequency and the measured frequency obtained from the watch by a micromotor.
The variations of this difference can be read on a scale which indicates the running of the watch. This reading must be effected by an operator which limits the use of this apparatus in automated installations.
There also exists apparatus having digital display, and sometimes analog, which after having preliminarily placed the two frequencies in phase, measures and memorizes the phase difference between them over a determined period of time. Such apparatus is very sensitive to parasitic conditions of detection and to the perturbations of mechanical watches.